Production of sulfur



Feb. 27, 1962 P. URBAN ET AL PRODUCTION OF SULFUR Filed July 5, 1960 N\t m \ssu mm 39: m n Q oEm am em om m s N VE N TORS;

Peter Urban Les/er 6. Massey A T TOR/KEYS 3,023,088 PRODUCTHON F SULFURPeter Urban, Northbrooir, and Lester G. Massey, Arlington Heights, Ill,assignors to Universal Oil Products Company, Des Piaines, lit, acorporation of Delaware Filed July 5, 1960, Ser. No. 40,840 6 Claims.(Cl. 23-226) This application is a continuation-impart of our copendingapplication Serial No. 554,591, filed December 21, 1955, now abandoned.

This invention relates to a process for the production of sulfur andparticularly to a process for producing sulfur from hydrogen sulfide. Inaddition, the invention also relates to a process for purifying a gasstream by removing hydrogen sulfide from said stream.

In many industrial processes, large amounts of sulfur are wasted bybeing vented to the atmosphere as hydrogen sulfide. Typical of these areprocesses for preparing various petroleum products, coking of coal,steel manufacture and others. In many cases, the sulfur is a contaminantin the ultimate desired product and is converted to hydrogen sulfideduring processing and disposed of in that form. Besides being wasteful,venting hydrogen sulfide to the atmosphere creates a nuisance which mustbe abated in many communities to conform with local regulations.

Several solutions to this problem have been put into effect and thesemostly have been used to abate the nuisance rather than to conservesulfur. The processes are usually difiicult to eifect and rather costlyand usually consist of converting the hydrogen sulfide to sulfur orsulfuric acid or some other salable form. One such solution has been toseparate the hydrogen sulfide from the main stream by such means as anabsorber employing an alkaline liquid such as an amine or metalhydroxide solution in countercurrent contact with the hydrogen sulfidecontaining gas. The absorbing liquid is then stripped of H 8 and H 8 ispartially burned to from S0 and water and the remaining H 5 is reactedwith the S0 to produce sulfur and water. The reaction is effected athigh temperatures employing a heterogeneous catalyst such as bauxite andpreferably at high pressure. This method has many unsatisfactoryfeatures including the expense and difficulty of concentrating H S bymeans of an alkaline solution with subsequent stripping, the use ofheterogeneous catalysts which are not too well suited to chemicalprocesses resulting in solid products, the difficulty of using corrosivematerials such as water-S0 mixtures at high temperature and, in fact,the difiiculty of employing high temperatures. It is an object of thisinvention to provide a novel process for recovering substantially puresulfur from a gas stream containing H 8 or mercaptans. Because of thegreat abundance of H 8 containing gas streams, this invention will bedescribed primarily in relation to this particular compound. The processof this invention overcomes the difficulties hereinbefore enumerated byproviding a simple, liquid phase, low temperature, non-catalytic processwhich results in large conversions of hydrogen sulfide to substantiallypure sulfur.

One embodiment of this invention resides in a process for the productionof sulfur which comprises absorbing sulfur dioxide and hydrogen sulfidein a carboxamide having the generic formula:

in which R, R and R are selected from the group consisting of hydrogenand alkyl radicals and having from about 0.5% to about 40% by volume ofwater dissolved therein, reacting the sulfur dioxide and hydrogensulfide in contact with said solvent, thereby forming sulfur, andseparating the sulfur from said solvent.

A specific embodiment of the invention is found in a process for theproduction of sulfur which comprises absorbing sulfur dioxide andhydrogen sulfide in a solvent comprising dimethylformamide, and havingfrom about 0.5% to about 40% by volume of water dissolved therein,reacting the sulfur dioxide and hydrogen sulfide in contact with saiddimethylformamide, thereby forming sulfur and separating the sulfur fromsaid solvent.

Other objects and embodiments referring to alternative carboxamideshaving the generic formula hereinabove set forth will be found in thefollowing further detailed description of the invention.

Briefly, the process of this invention provides for effecting thereaction between sulfur dioxide and hydrogen sulfide to form sulfur andwater while these two reactants are absorbed in a common liquid medium.By providing for 'such solution or absorption, the molecules areapparently brought into close proximity with others so thatreaction'scan occur more readily between them. In the process of this invention,the reaction occurs Without a catalyst substantially to completion evenat ambient temperatures in contrast to the process employing a vaporphase which requires high temperatures and a catalyst and which resultsin low conversions compared with the present process.

The solvent employed in this invention must have certaincharacteristics. Since a certain amount of water is required for thereaction to proceed rapidly, as will be hereinafter demonstrated, watermust necessarily be soluble in the solvent to some significant extent.Another characteristic is that the solvent must be capable of absorbingor dissolving both hydrogen sulfide and sulfur dioxide. Anotherrequirement of the solvent, although one that is easily met, is that itmust not dissolve large quantities of sulfur inasmuch as a solventhaving this characteristic would introduce another step in the process,namely recovering dissolved sulfur from the solvent.

Two distinct types of solvent may be used. The first is a solventmiscible in all proportions with water and when such a solvent is used,means must be provided to remove excess water from the solvent so thattoo much dilution does not occur. The other type of solvent is one whihcdissolves only limited quantities of water. A solvent with limitedmiscibility with Water, to be used in this invention, must be capable ofdissolving the necessary quantities of water to be hereinafter describedand preferably is saturated within the desired water concentrationrange. When such a solvent is used, the excess water which results fromthe reaction may be removed simply by drawing otf the aqueous phase.

It has now been discovered that not all organic solvents are suitablefor the production of sulfur, certain oxygenated organic compounds suchas the glycols although effective in some respects in forming sulfurpossess the disadvantage of having the sulfur thus formed in aflocculent or tacky state which is difficult to recover by thecommercial methods of separation. The sulfur formed by the use ofglycols as the solvent in this process is difiicult to separate byfiltration. For example, solutions of sulfur suspended in diethyleneglycol or methylene glycol when subjected to filtration resulted ineither the solutions passing through a filter without leaving anysulfur, or, after a period of time, said suspensions would clog thefilter completely before any substantial amount of solution had passedthrough. However, in contradistinction to this, we have now discoveredthat "aoaaoss when certain organic compounds such as carboxamides areutilized as the organic solvent in the process of this invention, thesulfur which is produced is crystalline in form as contrasted to theamorphous form of sulfur produced when glycols are used as solvents. Thesulfur crystals forr'ned when using a carboxamide as the organic solventare large and readily filterable, whereas the sulfur crystals, whenusing glycols as the organic solvent, form into some type of gelatinous,compressible mass. However, this mass is tacky in contrast to the hardcrystals hereinbefore set forth and thus cannot be readily filtered. Theparticular organic compounds utilizable in this process, consisting ofcarboxamides having the generic formula:

ii R'CN\ in which R, R and R are selected from the group consisting ofhydrogen and alkyl radicals containing from 1 to 4 carbon atoms, includeformamide, acetamide, propionamide, n-butyramide, isobutyramide,N-methylformamide, N,N-dimethylformamide, N-ethylformamide,N,N-diethylformamide, N-propylformamide, N,N-dipropylformamide,N-butylformamide, N,N-dibutylformamide, N-methylacetamide,N,N-dimethylacetamide, N-ethylacetamide, N,N- diethylacetamide,N-propylacetamide, N,N-dipropylacetamide, N-butylacetamide,N,N-dibutylacetamide, N-propionamide, N,N-dimethylpropionamide,N-ethylpropionamide, N,N-diethylpropionamide, N-propylpropionamide,N,N-dipropylpropionamide, N-butylpropionamide, N,N dibutylpropionamide,etc.

The process of this invention may be best described with reference tothe accompanying drawing which is intended to be illustrative of theinvention rather than limiting on its broad scope. g

In the drawing, H 8 or H S-containing gas from any source such as thosehereinbefore described is introduced through line 2 into the lowerportion of absorber 1. This gas may be, for example, the normallygaseous material in the efiluent from a petroleum desulfurization orreforming process, in which case it is desirable to recirculate thehydrogen in the gas, but to remove the hy drogen sulfide from it sincehydrogen sulfide has an adverse effect upon the catalysts employed insuch process. In absorber 1, the rising hydrogen sulfide is mixed withwhich is introduced into the lower portion of of absorber 1 through line3 and the mixture is contacted with a descending water-containingcarboxamide stream. Absorber 1 will contain internal means for effectingintimate contact between a rising gas stream and a descending liquidstream such as, but not limited to, perforated plates, bubble capplates, turbo-grid trays, packing, screens or any other conventionaldevice for causing such contact. The carboxamide in this embodiment isintroduced into the upper portion of absorber 1 through line 9 and isobtained as will be hereinafter discussed.

The water for such an absorber may be introduced commingled with thecarboxamide stream or preferably in a separate stream disposed above thecarboxamide stream such as through line 10. The purpose of this is toremove carboxamide from the hydrogen sulfide-free gas stream dischargingfrom the top of absorber 1 through line 4. This not only is conservativeof carboxarnide but prevents adverse effects which such solvent mighthave as an impurity in the gas stream.

As the carboxamide and water descend through absorber 1 they absorbhydrogen sulfide and sulfur dioxide. The carboxamide and water aremaintained at a temperature of from about 0 to about 120 C. or higherand preferably from about to about 100 C. The only temperaturelimitation on this process is that the temperature must be such as tohave a liquid phase solvent at absorber conditions. When maintained atthese conditions, the absorbed hydrogen sulfide and sulfur dioxide reactto form pure sulfur and Water. The resultant stream discharging from thebottom of absorber 1 through line 5, therefore, contains carboxamidesuch as those hereinbefore described, water, sulfur, and sometimesunreacted hydrogen sulfide and sulfur dioxide. It should be mentionedhere that the selection of a suitable solvent and optimum operatingconditions will cause substantially complete reaction ofhydrogen'sulfide with sulfur dioxide so that the residual unreactedcomponents in the stream discharging from absorber 1 will be negligible.The material passing through line 5 passes to sulfur removal zone 6wherein the sulfur is removed from the stream and thereafter passed outto a'recovery zone, not shown, through line 12. When the sulfur productis solid it may be removed by filtration, centrifugally, by settling orany other known means of removing solid particles from a liquid. Thesulfur may be removed as a liquid when the sulfur removal zone is aliquid when the sulfur removal zone is at a sufliciently hightemperature, in which case it may simply be drawn off from the totalliquid as a separate immiscible phase.

The sulfur-free liquid passes through line 7 to water separator 8wherein the water formed in the reaction of H 8 with S0 is removed toprevent a build-up of water in the circulating solvent stream. Waterseparator 8 may consist merely of a settling zone when the solventemployed dissolves only limited quantities of water. When the solvent ismiscible with water to too great an extent, then water removal zone 8must separate water from the solvent by some other means such asfractionation, evaporation, hydration of salts, etc. Water separator 8may separate water only to the extent that it was added by the reactionin which case water will be withdrawn through lines 10 and 11 and thedesired water-solvent mixture will pass to the top of absorber 1 vialine 9. Water separator 8 may, however, separate more water from thesolvent than what was added by the reaction in which case some water iswithdrawn via line 11 but some is added to the upper portion of absorber1 via line 10 to scrub solvent from the'exit gas as hereinbeforedescribed.

As will be hereinafter demonstrated, the solvent of this inventionpreferably contains from about 10.0% to about 40% by volume of water. Itis preferred that the solvent employed have limited water solubility butit must dissolve at least 0.5% and preferably not more than 40% water atthe temperature conditions in absorber 2. As hereinbefore stated, acarboxamide having these characteristics may conveniently be used sincethe water of reaction can be separated by settling and an elaboratefractionation zone is not required.

In addition to the continuous process hereinbefore described the processof this invention may also be effected in a batch type operation. When abatch type operation is used the desired carboxamide and the water areplaced in an appropriate apparatus following which the sulfur dioxideand hydrogen sulfide are then bubbled through the solution. After apredetermined period of time has elapsed the solution containing thecrystalline sulfur is then subjected to filtration whereby the sulfur isseparated from the carboxamide and water.

The following examples are given to illustrate the process of thepresent invention which, however, are not intended to limit thegenerally broad scope of the present invention in strict accordancetherewith.

Example I In this experiment anhydrous dimethylformamide was utilized asthe organic solvent. The dimethylformamide was divided into threeseparate portions and water was added to each of the dimethylformamideportions to bring the solvent to the desired water content, theresulting solutions containing 10%, 20% and 30% by volume of waterrespectively. Following this each portion of the solvent was thendivided into two aliquots and sulfur dioxide was added toone aliquot ofeach water concentration by bubbling the gas therethrough for a periodof about five minutes. The sulfur dioxide content was then determined byiodine-titration, the aliquot portion of the by volume of waterconcentration containing 1.3% by weight of sulfur dioxide, the 20% waterportion contained 1.1% and the 30% water portion contained 0.9% byweight of sulfur dioxide. Hydrogen sulfide gas was bubbled into theother aliquot of the preselected solvent containing water for a periodof from about 10 to about 20 minutes. This longer time for absorption ofhydrogen sulfide is due to the fact that the solubility of hydrogensulfide in the solvents is much less than that of sulfur dioxide.Following this the concentration of the hydrogen sulfide in the solventwas also determined by iodinethiosulfate titration, the 10% waterportion containing 0.6% by weight of hydrogen sulfide, the 20%water-dimethylformamide portion contained 0.6% and the 30%water-dimethylformamide portion contained 0.5% by weight of hydrogensulfide.

The two aliquots of each of the different water concentrations werecombined in graduated cylinders and the formation of sulfur therefromobserved. In the cylinder containing the 10% water-dimethylformamidesolution pratically all of the sulfur precipitated out in crystallineform at the end of two minutes. The cylinder containing the 20%Water-dimethylformamide solution showed a considerable precipitation ofsulfur at the end of four minutes. At the end of eight minutes both ofthe dimethylformamide solutions containing 10 and 20% water had settledall of the sulfur while the dimethylformamide solution containing 30%water had settled to a considerable extent.

At the sarne time that the above experiments were being performed asimilar experiment utilizing triethylene glycol was also run in a mannersimilar to that set forth above. That is, triethylene glycol containingabout 24% Water was divided into two portions, one portion having sulfurdioxide gas bubbled therethrough while the other portion had hydrogensulfide gas bubbled therethrough. The aliquot portions Were combined andmixed. At the end of eight minutes, during which time the sulfur in thedimethylformamide solutions had settled, the sulfur formed in thetriethylene glycol solution still remained in a suspended state.

Example 11 The carboxamide which is used in this example comprisesanhydrous diethylform-amide. The carboxamide is divided into threeportions and Water added thereto so that the final solution contains10%, 20% and 30% Water by volume, respectively. Each of the threesolutions is divided into two aliquot portions. Sulfur dioxide gas isbubbled through one of the aliquot portions while hydrogen sulfide gasis bubbled through the other. The two portions are combined and mixedthereby causing the formation of sulfur. The sulfur will precipitate ina crystalline form within a relatively short period of time and iseasily separable from the solution by conventional means such asfiltration.

Example III Dimethylacetamide is treated with Water so that threeportions will contain 10%, 20% and 30%, respectively. Each of thewater-dimethylacetamide solutions is divided into two aliquot portions,one portion having sulfur dioxide gas bubbled therethrough while theother portion has hydrogen sulfide gas bubbled therethrough. Aftercompletion of the addition of sulfur dioxide and hydrogen sulfide to thealiquot said aliquot in each water concentration range are combined. Thesulfur thus produced will precipitate in a crystalline state in each ofthe solutions within a relatively short period of time and will beeasily separable by filtration.

Example IV In this experiment anhydrous diethylacetamide is treated in amanner similar to that set forth in the above examples, that is, threesolutions containing 10%, 20% and 30% by volume of water, respectively,are prepared. Each of these water-diethylacetamide solutions are dividedinto two aliquot portions and are treated with hydrogen sulfide gas andsulfur dioxide gas. After completion of the gas addition the twoportions in each water range are combined and mixed. The sulfur thusproduced will precipitate in a crystalline form and will be easilyseparable by filtration.

Example V In this experiment a predetermined amount ofdimethylpropionamide is divided into three portions and water addedthereto so that the total content of water is 10%, 20% and 30% byvolume, respectively. Each of the resulting solutions is divided intotwo aliquot portions and sulfur dioxide gas is bubbled through oneportion while hydrogen sulfide gas is bubbled through the other portion.Upon completion of the gas addition the two portions are combined. Thesulfur, as in the solutions described in the above examples precipitatein a crystalline form and will be -easily separable by conventionalmeans such as filtration.

We claim as our invention:

1. A process for the production of sulfur which comprises absorbingsulfur dioxide and hydrogen sulfide in a solvent comprising acarboxamide having the generic formula:

in which R, R and R are selected from the group consisting of hydrogenand alkyl radicals containing from 1 to 4 carbon atoms, and having fromabout 0.5% to about 40% by volume of water dissolved therein, reactingthe sulfur dioxide and hydrogen sulfide in contact with said solvent,thereby forming sulfur, and separating the sulfur from said solvent.

2. A process for the production of sulfur which coma solvent comprisingdimethylformamide, and having from about 0.5% to about 40% by volume ofwater dissolved therein, reacting the sulfur dioxide and hydrogensulfide in contact with said dimethylformamide, thereby forming sulfur,and separating the sulfur from said solvent.

3. A process for the production of sulfur which comprises absorbingsulfur dioxide and hydrogen sulfide in a solvent comprisingdiethylformamide, and having from about 0.5 to about 40% by volume ofwater dissolved therein, reacting the sulfur dioxide and hydrogensulfide in contact with said diethylformamide, thereby forming sulfur,and separating the sulfur from said solvent.

4. A process for the production of sulfur which comprises absorbingsulfur dioxide and hydrogen sulfide in a solvent comprisingdimethylacetamide, and having from about 0.5% to about 40% by volume ofwater dissolved therein, reacting the sulfur dioxide and hydrogensulfide in contact with said dimethylacetamide, thereby forming sulfur,and separating the sulfur from said solvent.

5. A process for the production of sulfur which comprises absorbingsulfur dioxide and hydrogen sulfide in a solvent comprisingdiethylacetamide, and having from about 0.5% to about 40% by volume ofwater dissolved therein, reacting the sulfur dioxide and hydrogensulfide in contact with said diethylacetamide, thereby forming sulfur,and separating the sulfur from said solvent.

6. A process for the production of sulfur which com- 'spzsps's dissolvedtherein, reacting the sulfur dioxide and hydrogen sulfide in contactwith said dimethylpropionamide, thereby forming sulfur, and separatingthe sulfur from said solvent.

References Cited in the file of this patent UNITED STATES PATENTS Blohmet a1. Apr. 24, 1951 Townsend Apr. 7, 1959 FOREIGN PATENTS Great BritainAug. 3, 1955

1. A PROCESS FOR THE PRODUCTION OF SULFUR WHICH COMPRISES ABSORBINGSULFUR DIOXIDE AND HYDROGEN SULFIDE IN A SOLVENT COMPRISING ACARBOXAMIDE HAVING THE GENERIC FORMULA: